The present invention relates to a sheet delivery apparatus for extracting, from sheets printed by a printing unit in a sheet-fed offset rotary printing press and stacked on the pile board of a delivery device, every predetermined number of sheets as a printed sample or an inappropriate sheet which occurs at the start of printing or due to a printing registration error without stopping the printing press.
As shown in Japanese Patent Laid-Open No. 58-047749, a conventional sheet delivery apparatus includes a sheet loading device on which printing sheets are stacked, a delivered sheet receiver for a printed sample which is arranged downstream of the sheet loading device in the sheet convey direction, a switching cam arranged above the sheet loading device, and a fixing cam arranged above the delivered sheet receiver. In this structure, the switching cam is retreated from the traveling path of a delivery pawl by switching. When the traveling delivery pawl abuts against the fixing cam, it releases the sheet. The sheet is delivered not onto the sheet loading device but onto the delivered sheet receiver.
As shown in Japanese Patent Laid-Open No. 2000-62134, a sheet delivery apparatus is proposed which includes a pile board on which a sheet gripped by a sheet delivery pawl and conveyed by the travel of a delivery chain is to be stacked, and a receiving plate for a delivered sample sheet which is arranged most downstream in the sheet delivery chain. As shown in Japanese Patent Laid-Open No. 63-87469, a sheet delivery apparatus is proposed which includes a lay which is set upright or laid down by a handle operation and aligns the leading edge of a sheet stacked on a board receiving plate when it is set upright, and a sheet receiver which is interlocked with the laying operation of the lay to enter a sheet falling passage in order to regulate falling of the sheet onto the board receiving plate and receive the sheet. In this structure, while the sheet receiver receives a sheet, one of the sheets stacked on the board receiving plate is extracted as a printed sample.
Of the three conventional sheet delivery apparatuses described above, in the first and second apparatuses, the delivered sheet receiver or receiving plate for the sample sheet is arranged downstream of the sheet loading device in the sheet convey direction. Thus, the sheet which is to be delivered to the delivered sheet receiver or receiving plate passes above the sheet loading device. At this time, if the trailing edge of the sheet hangs due to the instability of the sheet or waving, the hanging trailing edge comes into slidable contact with the surface of the upper most one of the sheets stacked on the sheet loading device to damage the surface of the sheet, thus causing wasted paper. In the third apparatus described above, when a printed sample is to be extracted, it comes into slidable contact with the upper surface of the sheet immediately under it to damage the upper surface of the sheet, thus causing wasted paper.